Rubber goods such as tire treads often are made from elastomeric compositions that contain one or more reinforcing materials such as, for example, particulate carbon black and silica; see, e.g., The Vanderbilt Rubber Handbook, 13th ed. (1990), pp. 603-04.
Good traction and resistance to abrasion are primary considerations for tire treads; however, motor vehicle fuel efficiency concerns argue for a minimization in their rolling resistance, which correlates with a reduction in hysteresis and heat build-up during operation of the tire. These considerations are, to a great extent, competing and somewhat contradictory: treads made from compositions designed to provide good road traction usually exhibit increased rolling resistance and vice versa.
Filler(s), polymer(s), and additives typically are chosen so as to provide an acceptable compromise or balance of these properties. Ensuring that reinforcing filler(s) are well dispersed throughout the elastomeric material(s) both enhances processability and acts to improve physical properties. Dispersion of fillers can be improved by increasing their interaction with the elastomer(s). Examples of efforts of this type include high temperature mixing in the presence of selectively reactive promoters, surface oxidation of compounding materials, surface grafting, and chemically modifying the polymer, typically at a terminus thereof.
Various elastomeric materials often are used in the manufacture of vulcanizates such as, e.g., tire components. In addition to natural rubber, some of the most commonly employed include high-cis polybutadiene, often made by processes employing catalysts, and substantially random styrene/butadiene interpolymers, often made by processes employing anionic initiators. Functionalities that can be incorporated into polymers prepared by one of these processes often cannot be incorporated into polymers prepared by the other type.
Cis-1,4-polydienes produced with lanthanide-based catalysts often have a linear structure, which is believed to provide improved tensile properties, improved abrasion and fatigue resistance, and reductions in hysteresis loss. Such cis-1,4-polydienes thus are particularly suitable for use in tire components such as sidewalls and treads.